Evolution myths: Evolution produces perfect organisms

It’s a theme endlessly repeated in wildlife documentaries. Again and again we are told how perfectly animals are adapted to their environment. It is, however, seldom true.

Take the red squirrel, which appeared to be perfectly adapted to its environment until the grey squirrel turned up in the UK and demonstrated that it is in fact rather better adapted to broadleaf forests.

There are many reasons why evolution does not produce perfect “designs”. Natural selection only requires something to work, not to work as well as it could. Botched jobs are common. The classic example is the panda’s “thumb”, a modified wrist bone that the animal uses like an opposable thumb to grasp bamboo. It’s far from the ideal tool for the job, but since the panda’s true thumb is fused into its paw, the panda had to settle for a clumsier alternative.

Evolution is far more likely to reshape existing structures than throw up novel ones. The lobed fins of early fish have turned into structures as diverse as wings, hoofs and hands. What this means is that we have five fingers because amphibians had five digits, not because five fingers is necessarily the optimal number for the human hand.

Many groups haven’t evolved features that would make them better adapted. Sharks lack the gas bladder that allows bony fish to precisely control their buoyancy, and instead have to rely on swimming, buoyant fatty livers and, occasionally, gulping air. Mammals’ two-way lungs are far less efficient than those of birds, in which the air flows …